Create map, filter and reduce array functions

array-functions.js

// MAP
function map(array, callbackFunction) {
    var newArray = [];
    for (var i = 0; i < array.length; i++) {
        newArray[i] = callbackFunction(array[i]);
    }
    return newArray;
}

// Test
var input = [1, 2, 3, 4];
var output = map(input, function(value) {
    return value + 1;
})


// FILTER
function filter(array, callbackFunction) {
    var newArray = [];
    for (var i = 0; i < array.length; i++) {
        if (callbackFunction(array[i])) {
            newArray.push(array[i])
        }
    }
    return newArray;
}

// Test
var input = [1, 2, 3, 4];
var output = filter(input, function(value) {
    return value % 2 === 0;
})


// REDUCE
function reduce(array, callbackFunction, startingValue) {
    var result = startingValue
    for (var i = 0; i < array.length; i++) {
       result = callbackFunction(result, array[i]);
    }
    return result;
}

// Test
var input = [1, 2, 3, 4];
var output = reduce(input, function(sum, value) {
    return sum + value;
}, 0)